Gallium nitride based light-emitting device

ABSTRACT

A manufacturing method and a thus produced light-emitting structure for a white colored light-emitting device (LED) and the LED itself are disclosed. The white colored LED includes a resonant cavity structure, producing and mixing lights which may mix into a white colored light in the resonant cavity structure, so that the white colored LED may be more accurately controlled in its generated white colored light, which efficiently reduces deficiency, generates natural white colored light and aids in luminous efficiency promotion. In addition to the resonant cavity structure, the light-emitting structure also includes a contact layer, an n-type metal electrode and a p-type metal electrode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a light emitting device and amanufacturing method for a light-emitting device (LED), and particularlyto a highly efficient light-emitting structure and a manufacturingmethod for an LED. In particular, the light-emitting structure proposedherein is based on the Group-III GaN-based materials and has a resonantcavity structure used to enhance luminous efficiency of the generatedlight therefrom.

2. Descriptoin of Related Art

Light-emitting devices (LEDs) have been developed and on the market foryears and are useful in providing lights as generally recognized. Theuse of LEDs in digital watches and calculators are well known. As wesee, it may also find other important applications in communications andother areas, such as mobile phone and some appliances. Recently, thereis a trend that LEDs be further applied to ordinary human livingutilization, such as large panels, traffic lights and lightingfacilities and the perspective thereof are looking good. Therefore, LEDsare increasingly playing an important role in our daily life anddeserving more efforts. As is transparent to those skilled in the art,LEDs are produced based on some semiconductor materials and emits lightsby dint of the behaviors aroused in the semiconductor materials in thepresence of an applied electrical bias.

In particular, an LED gives off a light by a light-emitting structuretherein generally composed of some Group-III (compound) semiconductorowing to its stronger inclination of recombination of electrons andholes. In principle, an LED is basically a well-known p-n junctionstructured device, i.e., a device having a p region, an n region and atransient region therebetween. With a forward voltage or current biasapplied, the majority of carriers in the p or n regions driftrespectively towards the other region (through the transient region) inthe device due to the energy equilibrium principle and a current isaccounted for, in addition to the general thermal effects. Whenelectrons and holes jumped into a higher value of energy band with theaid of electrical and thermal energy, the electrons and the holesrecombine there and give off lights when they randomly and spontaneouslyfall back to a reduced energy state owing to thermal equilibriumprinciple, i.e. spontaneous emission.

Afterwards, the concept and structure widely used in semiconductordevice of the multi-quantum well (MQW) layers are introduced into an LEDstructure. Generally, the MQW layers are formed between the p and the nregions in the above-mentioned p-and-n structure, which forms theso-called “PIN” structure. With the aid of the MQW active layers, thepossibility of recombination of the electrons and holes in the p-njunction based device are efficiently enhanced and the luminousefficiency thereof is upgraded considerably. Further, the color of alight emitted from the LED may be controlled through a choice of thematerials, dopant concentration and layer thickness in the MQW layers.

However, the current LEDs are still not sufficient in brightness inserving as some light supplying facilities, and which has long been thecommon issue that all researchers in the field concern and desire toaddress.

In view of the foregoing problem, the inventors of the present inventionprovides a novel colored light emitting diode with a different structureso as to increase luminous efficiency of the currently used LED.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide alight-emitting structure and its manufacturing method for an LED whichmay usefully enhance its luminous efficiency without largely increasingcost.

To achieve the object, the present invention provides a light-emittingstructure for an LED, wherein the light-emitting structure comprises aresonant cavity. In one embodiment, the resonant cavity bordered by alower reflecting component, p-GaN based distributed Bragg reflector(DBR) and an upper reflecting component, a metal reflector or an n-GaNbased distributed Bragg reflector (DBR). Owing to the light resonationand the thus self-exciting of the emitted light in the LED device, thelight out of the LED device is efficiently enhanced with a fixedelectric power source.

To achieve the above-mentioned LED, the present invention also providesa manufacturing method for the light-emitting structure. In oneembodiment, the method comprises forming a buffer layer over asubstrate; forming an GaN based epitaxial layer over the buffer layer;forming an MQW active layer over the n-GaN based layer; forming a P-DBRover the MQW active layer; forming a p-GaN based epitaxial layer overthe P-DBR and etching away a portion of the n-GaN based layer, the MQWactive layer, the p-type DBR and the p-GaN based layer whereby anexposing region is formed on the n-GaN layer; and coating a metalreflector over a bottom side of the substrate.

Along with the high luminous efficiency, the resonant cavity utilizingthe metal reflector as the lower reflecting element may efficientlyreduce cost and simplify manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

To better understand the other features, technical concepts and objectsof the present invention, one may read clearly the description of thefollowing preferred embodiment and the accompanying drawings, in which:

FIG. 1 depicts schematically a manufacturing method of a preferredembodiment according to the present invention;

FIG. 2 depicts schematically a perspective diagram of a structure of alight-emitting structure of a preferred embodiment according to thepresent invention;

FIGS. 3 and 3A represent a particular example of the epitaxial structureshown in FIG. 2;

FIG. 4 depicts schematically a manufacturing method of a secondembodiment according to the present invention;

FIG. 5 depicts schematically a structure of a light-emitting structureof a second embodiment according to the present invention;

FIG. 6 depicts a particular example of the epitaxial structure shown inFIG. 5;

FIG. 7 depicts schematically a manufacturing method of a thirdembodiment according to the present invention;

FIG. 8 depicts schematically a manufacturing method of a fourthembodiment according to the present invention;

FIG. 9 depicts schematically a perspective diagram of a structure of afourth embodiment according to the present application;

FIG. 9A depicts schematically a structure of a device of the fourthembodiment according to the present application;

FIGS. 10 and 10A depict schematically a particular example of theepitaxial structure shown in FIG. 9;

FIG. 11 depicts schematically a manufacturing method of a fifthembodiment according to the present invention;

FIG. 12 depicts schematically a structure of a fifth embodimentaccording to the present invention;

FIG. 13 depicts a particular example of the epitaxial structure shown inFIG. 12; and

FIG. 14 depicts schematically a structure of a six embodiment accordingto the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to an improved light-emitting structurefor an LED in terms of luminous efficiency, wherein the light-emittingstructure comprises a resonant cavity. In a preferred embodiment, themanufacturing method for a high efficiency light-emitting device (LED)device according to the present invention comprises the following steps.In appreciating the preferred embodiment, please refer directly to FIG.1 to 3, wherein the reference numerals given in the corresponding deviceare also used in the recitation of the steps.

Step 1: forming a buffer layer 11 over a substrate 10, i.e., forming abuffer layer 11 over an upper surface 10 a of the substrate 10. Thesubstrate 10 may be such as sapphire, silicon carbide (SiC) and galliumnitride (GaN) for the consideration that a GaN based material is chosenthereon, The buffer layer 11 may be composed of some layers depending onchoice of design, such as a coarse grain nucleation layer made of GaNand an undoped GaN layer. The nucleation layer is a low temperaturelayer, i.e. formed under a low temperature condition, about 500-550° C.;has a thickness of 200-400 Å and will be referred to as an LT-GaN layerherein. The undoped GaN is a high temperature layer, formed under atemperature of 1020-1040° C. and has a thickness of 0.2-2 μm, and willbe termed as an HT-GaN layer. These buffer layers may be formed bymolecular beam epitaxy (MBE), metal organic chemical vapor deposition(MOCVD) and some other suitable technologies, currently in existence orset forth in the future. The application of the buffer layer 11 is aimedto lattice matching between the substrate and the epitaxial layer formedthereon, and some other reasons.

Step 2: forming an n-GaN based epitaxial layer 13 over the buffer layer11. It may be executed by such as MBE and MOCVD. In forming such n-GaNbased epitaxial layer, the temperature is 1020° C.-1040° C. and theformed thickness is 2-8 μm.

Step 3: forming an MQW active layer 14 over the n-GaN based epitaxiallayer 13, wherein the MQW active layer 14 is chosen so that the MQWactive layer 14 may generate a light with a wavelength from 380 nm to600 nm.

Step 4: forming a p-type distributed Brag reflector (DBR) 15 over theMQW active layer 14. As well known to those persons skilled in the art,a DBR is a multi-layer structure formed for reflection of a light. In apreferred embodiment of the present invention, the p-type DBR 15 isAlGaN/GaN. The thickness thereof is 0.1-0.5 μm and the processtemperature therefor is 960-1000° C. The reflectance of the p-type DBRmay be chosen between 50 and 80%.

Step 5: forming a p-GaN based layer 16 over the p-type DBR 15 andetching away a portion of the n-GaN layer 13, the MQW active layer 14,the p-type DBR 15 and the p-GaN based layer 16 whereby the n-GaN layer13 has an exposing region 13 a and an n-type electrode 17 may bedisposed over the exposing region 13 a and a p-type electrode 18 may bedisposed over the p-GaN layer 16. The p-GaN based layer 16 can be formedby such as MBE and MOCVD, under the process conditions of a temperatureof 1020° C.-1040° C. and a thickness is 2-8 μm. On the other hand, then- and p-type electrodes 17 and 18 may be formed by such as sputtering,vaporizing and E-gun technologies, and the adopted electrode materialmay be well-conductive metal of all appropriate kinds, such as aluminumand copper, and may preferably have good light transparency (to thelight generated from the device, i.e., 380 nm to 600 nm), such as a thinNi/Au layer (with the Ni layer formed first and the Au layer atop the Nilayer). It is to be noted that although the formations of the p-type andn-type electrodes 17, 18 are not recited in this step and FIG. 1, theyare in effect formed successively. In terms of the p-type and n-typeelectrodes, all embodiments explained here will not present them in thecorresponding drawings and description. As for the etching, it is notpresented in the corresponding drawing, FIG. 1. The suitable etchingmethod may be dry etching, such as chlorine plasma etching.

Step 6: coating a metal reflector 19 over a bottom side of the substrate10. The coating method may be such as sputtering, vaporizing and E-guntechnologies. In undertaking such a coating step, the bottom side of thesubstrate 10 may be polished to a reduced thickness, 50 μm to 300 μm,from a larger thickness and then coated with the metal reflector 19. Themetal reflector 19 is made of a suitable metal so that a specifiedreflector, such as one having a desired reflectivity, may be achievedand the reflectivity may be over 90%. The metal coating layer 19 has athickness of 50 Å to 10 μm and may be performed by electroplating,sputtering and some other suitable technologies.

In FIGS. 2 and 2A, a light-emitting structure according to the preferreddevice embodiment of the present invention is recited which correspondsto the preferred method embodiment shown in FIG. 1. The light emittingdevice comprises a metal reflector 19, a substrate 10, a buffer layer11, an n-GaN based layer 13, an MQW active layer 14, a p-type DBR 15, acontact layer 16, an n-type metal electrode 17 and a p-type metalelectrode 18, wherein the region bordered by the two reflectingcomponents, the metal reflector 19, and the p-type distributed Braggreflector (DBR) 15 forms a resonant cavity. In the figure, the circlewith arrows indicates the behavior of the light resonation in theresonant cavity, and that will hold for all drawings in the presentinvention. In the device, the substrate 10 may be such as sapphire,gallium nitride (GaN) and silicon carbide (SiC). The metal reflector 19coated on a lower surface 10 b of the substrate 10 has a reflectance oflarger than 90%. The buffer layer 11 is provided as an intermediatelayer between the substrate 10 and the MQW active layer 12 for somereasons, such as better lattice matching. As also described in theabove, the buffer layer 11 may be composed of some layers. The MQWactive layer 14 is chosen so that the layer 14 may generate a lighthaving a wavelength of 380 nm to 600 nm once an electrical bias is fedinto the LED device. The contact layer 16 is a p-GaN based layer andformed over the p-type DBR 15 for contact with a corresponding electrode18. The p-type metal electrode 18 is disposed over the p-GaN layer 16for electricity feed, while the n-type metal electrode 17 is disposedover an exposing region 13 a of the n-GaN layer 13. The n-GaN basedlayer 13, the MQW layer 14 and the P-DBR layer 15 jointly form a P-I-Nlight generating unit, which is familiar to those persons skilled in theart and will not be explained here.

To obtain a specific color of the emitted light from the LED device, theMQW active layer 14 should be carefully chosen. In accordance with thegenerally known chromaticity diagram, when the MQW active layer emits alight with a wavelength of 465 nm to 485 nm upon an applied electricbias, the LED is a blue colored LED. When the MQW active layer 14 emitsa light with a wavelength of 495 nm to 540 nm upon an applied electricbias, the LED is a green colored LED. When the MQW active layer 14 emitsa light with a wavelength of 560 nm to 580 nm upon an applied electricbias the LED is a yellow colored LED. Of course, the MQW active layer 14may emit a light having a wavelength between 380 nm-600 nm but otherthan the above range and become some other colored LED, which dependsupon the choice of the MQW layer 14.

To completely form a marketed LED, wire bonding and packaging arenecessary on the light-emitting structure. Since these steps are wellknown to those persons skilled in the art, the description of therelated technology is omitted here.

In FIGS. 3 and 3A, a particular example of the device depicted in FIG. 2is shown. In the example, the first and second layers 111 areLT-GaN/HT-GaN buffer layers, in which the former has a thickness of30-500 Å while the latter 0.2-0.5 μm. The third layer 131 is an n-GaNbased semiconductor layer with a thickness of 2-6 μm. The fourth layer141 is an InGaN/GaN MQW layer. The fifth layer 151 is a p-AlGaN/GaN DBR.The sixth layer 161 is p⁺-GaN based semiconductor with a thickness of0.2-0.5 μm, wherein the heavy dopant concentration of the sixth layer161 is aimed at better ohmic contact with the upper metal electrode (notshown).

Lower to the above layers are a substrate 101 and a metal reflector 191,wherein the metal reflector 191 is coated below the substrate 101.Specifically, the substrate 101 may be sapphire, SiC or GaN. Inmanufacturing process, the substrate 101 first has a thickness of300-500 μm in the process of the growth of those epitaxial layers overthe substrate 101. After the epitaxial layers are formed, the substrate101 is polished at its bottom side to a thickness of 50-300 μm and ametal reflector 191 is coated thereon. The metal reflector 191 may beAg/Al, i.e., first coated with Ag and then Al so that Ag material willnot expose, or Ag, or any other metal, and may have a thickness of 50 Åto 10 μm.

Now the description will be made to a second method embodiment accordingto the present application, and please refer directly to FIG. 4. Thesecond method embodiment is the same as the preferred embodiment exceptfor the step, Step 6′. Step 6′: coating a transparent contact layer(TCL) with a suitable thickness over the contact layer, p-GaN basedlayer, succeeding to Step 5. In terms of material used, the TCL may bemade of Ni/Au and other suitable transparent (for the generated lightfrom the light-emitting structure, such as a light with a wavelength of380-600 nm) and conductive materials and may be an n-TCL (n-doped) or ap-TCL (p-doped). In fact, the TCL may be a doped metal oxide, such asdoped ZnO, which may be referenced to U.S. patent application—(pleaserefer to the two our co-filing cases, after they obtain applicationnumbers), co-pending with the present invention application and assignedto the same assignee of the present invention.

The second device embodiment according to the present invention ismanufactured by the second method embodiment and provided schematicallyas FIG. 5. It is to be noted that the TCL 20 is added for compensatingfor the lower mobility of the majority of carriers, holes and uniformlyspreading the electrical charges in the neighborhood of the p-typeelectrode 18 to the entire contact layer, p-GaN based layer 16, and thuspromoting luminous efficiency of the device. Referring to FIG. 6, itillustrates a particular example of FIG. 5. As is with the p⁺-GaN basedlayer 161 of FIG. 3, the p-GaN based layer 161 is also heavily doped forbetter ohmic contact with the upper metal electrode (not shown) and maybe a p-InGaN or a p-AlInGaN layer.

Referring to FIG. 7 illustrating a third method embodiment of thepresent invention, which is composed by adding the second methodembodiment with a step, Step 8. Step 8: subjecting the TCL 20 to asurface treatment at its upper surface. Step 8 is executed forminimizing the portions of the generated light back off into thelight-emitting structure. The surface treatment applied may be forming aroughened surface or some particularly texturized surface on the TCLsurface, and the light extraction efficiency may be increased.

It is to be noted that Step 6′ and Step 7 in the second embodiment canbe executed in different sequence, and so can Step 6′ and Step 7 in thethird embodiment.

The fourth to the sixth embodiments according to the present inventionare different with the former three embodiments in design of theresonant cavity. Referring to FIG. 8 to 10A, a fourth embodimentaccording to the present invention is illustrated therein, wherein FIG.8 shows a method thereof, FIGS. 9 and 9A show a device thereof, andFIGS. 10 and 10A are a particular example of the device shown in FIGS. 9and 9A. In the embodiment, an N-DBR layer 32 is used as the lowerreflecting component in replace of the metal reflector in theabove-mentioned embodiments, and the method comprises the followingsteps.

Step 1 a: forming a buffer layer 31 over a substrate 30, i.e., forming abuffer layer 31 over an upper surface 30 a of the substrate 30. Thesubstrate 30 may be such as sapphire, SiC or GaN. Step 2 a: forming ann-DBR 32 over the buffer layer 31. Step 3 a: forming an n-GaN basedlayer 34 over the n-DBR 32. Step 4 a: forming an MQW active layer 35over the n-GaN layer 34, wherein the MQW active layer 35 is chosen sothat the layer 35 may emit a light having a wavelength of 380-600 nm.Step 5 a: forming a p-DBR 36 over the MQW active layer 35. Step 6 a:forming a p-GaN based layer 37 (for example, a p-GaN layer, a p-InGaNlayer or a p-AlInGaN layer) over the p-DBR 36 and etching away a portionof the n-GaN based layer 34, the MQW active layer 35, the P-DBR 36 andthe p-GaN layer 37 whereby an exposing region 34 a is formed on then-GaN based layer 34, an n-type electrode 38 may be disposed over theexposing region 34 a, and a p-type electrode 39 may be disposed over thep-GaN layer 37. In the method embodiment, the n-type DBR and the p-typeDBR are chosen below 90% in reflectance.

The device of the fourth embodiment according to the present invention,FIGS. 9 and 9A, includes a substrate 30, an n-DBR 32, an n-GaN layer 34,an MQW active layer 35, a p-DBR 36, a contact layer 37, an n-type metalelectrode 38 and a p-type electrode 39.

As compared to the former three embodiments, the fourth deviceembodiment is different in the resonant cavity, which is formed betweenthe n-DBR 34 and the p-DBR 36 (the metal reflector 19 and the P-DBR 15in the afro-mentioned embodiments), and the substrate 30 is not includedin the resonant path. In this case, the substrate 30 may be transparentor not transparent, such as silicon, which is contrary to thetransparent substrate 10 in the above embodiments.

Referring to FIGS. 10 and 10A, a particular example of FIGS. 9 and 9A isshown there. In the example, the first and second layer 311 is anLT-GAN/HT-GaN buffer layer, the third layer 321 is an n-AlGaN/GaN DBR,the fourth layer 341 is an n-GaN semiconductor layer having a thicknessof 2-6 μm, the fifth layer 351 is an InGaN/GaN MQW layer, the sixthlayer 361 is a p-AlGaN/GaN DBR and the seventh layer 371 is a p+-GaNbased semiconductor layer having a thickness of 0.2-0.5 μm. Theseepitaxial layers are formed over the substrate 301 having a thickness of300-500 μm.

Referring to FIG. 11 to 13 illustrating a fifth embodiment according tothe present invention. As shown in FIG. 11, the fifth method embodimenthas an extra step, Step 7 a, as compared to the fourth embodiment. Step7 a: forming a metal oxide layer 40 over the p-GaN layer 37, wherein thelayer 40 has a suitable thickness and is transparent to a visible lighthaving a wavelength of such as 380-600 nm. FIG. 12 shows a fifth deviceembodiment of the present invention, which corresponds to the method inFIG. 11. As mentioned in the above, some metal oxides may be used as theTCL. Accordingly, Step 7 a provides such a TCL.

Referring to FIG. 13, it illustrates a particular example of the fifthembodiment. In the example, all layers are the same as the correspondingones in the fourth embodiment except for the ZnO metal oxide layer 401,which may also be Al doped ZnO and has a thickness of 50 Å-50 μm.

It is to be noted that the metal oxide 40 may further beIn_(x)Zn_(1-x)O, Sn_(x)Zn_(1-x)O or In_(x)Sn_(y)Zn_(1-x-y)O basedmaterials, wherein 0≦X≦1, 0≦Y≦1 and 0≦X+Y≦1; or a metal oxide having anindex of refraction of all least 1.5; or n-type conductive or p-typeconductive metal oxide; or rare earth element doped metal oxide.

Referring to FIG. 14 illustrating a sixth embodiment of the presentinvention. In the embodiment, there is an extra step, Step 8, ascompared to the fifth embodiment. Step 8 a: subjecting the metal oxidelayer 40 to a surface treatment. That is, the region of the metal oxidelayer 40 not contacted with the p-type metal 39 is subject to a surfacetreatment so as to have a roughened surface 41 or a particularlytexturized surface.

It is to be noted that the epitaxial layers in the present invention maybe formed by self-texturing by sputtering, physical vapor deposition,ion plating, pulsed laser evaporation, chemical vapor deposition,molecular beam epitaxy technologies or some other suitable technologies.

While the invention has been described by way of example and in terms ofpreferred embodiments, it is to be understood that the invention is notlimited thereto since those skilled in the art may easily deduce someassociated modifications. For example, GaAs may be utilized in the PINstructure of the present invention and render the corresponding lightemitting device to emit a red colored light and the corresponding LED asa red colored LED. In fact, the present invention is intended to covervarious modifications and similar arrangements and procedures, and thescope of the appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

1-3. (canceled)
 4. A light-emitting structure for a light emitting diode(LED), comprising a resonant cavity structure, a contact layer, ann-type metal electrode and a p-type metal electrode, wherein: saidresonant cavity structure formed by a metal reflector, a substrate, abuffer layer, an n-GaN based layer, an MQW active layer and a p-typedistributed Bragg reflector (DBR), wherein and said substrate comprisessapphire; said contact layer being a p-GaN based layer and formed oversaid p-type DBR; said n-type metal electrode disposed over an exposinglayer of said n-GaN layer; and said p-type metal electrode disposed oversaid p-GaN layer; wherein said MQW active layer comprises a material sothat said MQW active layer generates a light with a wavelengthcomprising 380-600 nm in response to an applied electric power betweensaid n-type metal electrode and said p-type metal electrode.
 5. Thelight-emitting structure as in claim 4, wherein said substrate furthercomprises silicon carbide (SiC) and gallium nitride (GaN).
 6. Thelight-emitting structure as in claim 4, wherein said contact layerfurther comprises a p-InGaN and a p-AlInGaN layers, and said p-type DBRcomprises AlGaN/GaN.
 7. The light-emitting structure as in claim 4,wherein said metal reflector has a reflectance of greater than 90% andsaid p-type DBR has a reflectance of 50-80%.
 8. The light-emittingstructure as in claim 4, wherein the light-emitting structure furthercomprises a transparent contact layer (TCL) and said TCL is formed oversaid contact layer and transparent to a light having a wavelength of 380to 600 nm.
 9. A light-emitting structure for a light-emitting device(LED), comprising: a metal reflector on a bottom side of a substrate,wherein said metal reflector has a thickness of 50 to 10 μm and is madeof a conductive metal or metal alloy; an LT-GaN/HT-GaN buffer layerhaving a first formed LT-GaN buffer layer on said substrate and a thenformed HT-GaN buffer layer on said LT-GaN buffer layer, wherein saidLT-GaN buffer layer has a thickness of 30 to 500 while said HT-GaNbuffer layer with a thickness of 0.5 to 6 μm; an n-GaN semiconductorlayer having a thickness of 2 to 6 μm; an InGaN/GaN MQW active layer; ap-AlGaN/GaN distributed Bragg reflector (DBR); and a p⁺-GaN basedsemiconductor layer having a thickness of 0.2 to 0.5 μm; wherein saidsubstrate comprising sapphire and said MQW active layer emits a lightwith a wavelength comprising 380-600 nm in response to an appliedelectric power;
 10. The light-emitting structure as in claim 9, whereinsaid substrate further comprises silicon carbide (SiC) and galliumnitride (GaN), and wherein said metal reflector comprises Ag, Al andother metallic materials.
 11. The light-emitting structure as in claim9, wherein said p⁺-GaN based semiconductor layer further comprises ap-InGaN and a p-AlInGaN layers.
 12. The light-emitting structure as inclaim 9, wherein said p⁺-GaN based semiconductor layer is further coatedwith a transparent contact layer (TCL), and said TCL comprises Ni/Au andother conductive material transparent to a light having a wavelength of380 nm to 600 nm. 13-15. (canceled)
 16. A light-emitting structure for alight emitting diode (LED), comprising a substrate, a resonant cavitystructure, a contact layer, an n-type metal electrode and a p-type metalelectrode, wherein: said substrate comprising sapphire and having abuffer layer thereon; said resonant cavity structure formed over saidbuffer layer, comprising an n-type distributed Bragg reflector (DBR), ann-GaN based layer, a multi-quantum well (MQW) active layer and a p-typeDBR layers; said contact layer being a p-GaN based layer and formed oversaid p-type DBR; said n-type metal electrode disposed over an exposingregion of said n-GaN layer; and said p-type metal electrode disposedover said p-GaN based layer; wherein said MQW active layer comprises amaterial so that said MQW active layer generates a light with awavelength of 380 nm to 600 nm in response to an applied electric powerbetween said p-type electrode and said n-type electrode.
 17. Thelight-emitting structure as in claim 16, wherein said substrate furthercomprises silicon carbide (SiC), silicon (Si) and gallium nitride (GaN).18. The light-emitting structure as in claim 16, wherein said contactlayer further comprises a p-InGaN and a p-AlInGaN epitaxial layers. 19.The light-emitting structure as in claim 16, wherein said n- and p-DBRhave a reflectivity of less than 90%.
 20. The light-emitting structureas in claim 16, wherein said light-emitting structure further comprisesa TCL formed over said contact layer and conductive and transparent to alight having a wavelength of 380 to 600 nm.
 21. A light-emittingstructure for a light-emitting device (LED) comprised of an epitaxialstructure, comprising: an LT-GaN/HT-GaN buffer layer having a firstformed LT-GaN buffer layer on a substrate and a then formed HT-GaNbuffer layer on said LT-GaN buffer layer, wherein said LT-GaN bufferlayer has a thickness of 30 to 500 while said HT-GaN buffer layer has athickness of 0.5 to 6 μm; an n-AlGaN/GaN distributed Bragg reflector(DBR); an n-GaN semiconductor layer having a thickness of 2 to 6 μm; anInGaN/GaN MQW active layer; a p-AlGaN/GaN DBR; and a p⁺-GaN basedsemiconductor layer having a thickness of 0.2 to 0.5 μm; wherein saidsubstrate comprises sapphire and said MQW active layer emits a lightwith a wavelength comprising 380-600 nm in response to an appliedelectric power.
 22. The light-emitting structure as in claim 21, whereinsaid substrate further comprises silicon carbide (SiC), silicon (Si) andgallium nitride (GaN).
 23. The light-emitting structure as in claim 21,wherein said p⁺-GaN based semiconductor layer further comprises p-InGaNand p-AlInGaN layers.
 24. The light-emitting structure as in claim 21,wherein a transparent contact layer (TCL) is further formed over saidp⁺-GaN based semiconductor layer, wherein said transparent contact layer(TCL) comprising Ni/Au and other conductive material transmissible to alight with a wavelength of 380-600 nm, wherein said TCL has a thicknessso that said light may penetrate therethrough.